The Canyon of the Zopilote River and neighbouring area southward beyond the state
capital Chilpancingo and westward to the Sierra El Plateado cover 4383 km², situated
between Mexico City and Acapulco in Guerrero, a state along the Pacific coast of
south-western Mexico. The region is part of seven municipalities: Zumpango del Río,
Chilpancingo, Chichihualco, Tlacotepec, San Miguel Totolapan, Atoyac de Alvarez and Coyuca
de Benítez. It is in the Sierra Madre del Sur morphotectonic province and mainly in the
Pacific Ranges and Cuestas subprovince (including the Sierra de Igualatlaco), with the
northern lowlands in the Balsas Depression subprovince (Ferrusquía-Villafranca 1993).

The topography is generally mountainous, with c. 40% above 2000 m, and drainage mostly
to the Balsas River in the north. The minimum elevation in the north-east is 600 m, in the
north-west 2000 m. Important peaks ("cerros") include Yextla (2950 m) centrally,
and in the south-west Teotepec (3550 m), Jilguero (2850-2900 m) and Tlacotepec (3330 m).
Minimum elevations in the south-west and south-east are 800 m and 1600 m, within
watersheds draining directly to the coast.

The local weather is considerably influenced by the region's diverse topography. The
general climate changes with increasing elevation from hot and dry in the lowland interior
to warm to temperate and subhumid, to cool on the highest peaks. Generally there is a dry
season during winter and spring, with precipitation mostly in summer through autumn. In
the semi-arid area near Chilpancingo above Zopilote Canyon, the annual rainfall of 800 mm
occurs mainly in May-November, and the mean annual temperature is 24°C with a 4.5°C
oscillation and the extremes 5°C and 40°C; in May the diurnal fluctuation is 14°C
(Rzedowski 1978). Higher in the mountains, precipitation may be over 1600 mm and
temperatures become cooler, but the region includes many different restricted habitats,
for example related to rain shadows and the full compass of slope aspects.

Of the ten principal vegetation types in Mexico, seven occur in the region (Rzedowski
and Vela 1966; Rzedowski 1978; Fonseca and Lorea 1980). The varied topography and climate
have resulted in a diverse mosaic. Along a north-east to south-west transect from Mezcala
over the crest to Paraíso, the main formations are:

1. Deciduous tropical forest (500 m at Mezcala ascending to
Xochipala). Many species of Bursera are characteristic, such as B. bonetii, B.
longipes, B. morelensis, and columnar cacti especially in the canyon, such as Neobuxbaumia
mezcalaensis and Pachycereus weberi (P. gigas).

2. With increasing altitude develops a transitional forest very rich
in species, e.g. Ostrya virginiana, Cercocarpus macrophyllus, Juniperus
flaccida and Actinocheita potentillifolia mixed with Quercus spp. from
higher elevations. East of the transect near more arid Chilpancingo (1275 m) is
xerophilous scrub, where Quercus magnoliifolia has become shrub-like (Miranda
1947), and Agave cupreata occurs on warmer slopes.

5. Pine forest (above 2400 m) in less humid locales, with Pinus
herrerae, P. leiophylla, P. ayacahuite and P. pseudostrobus var. oaxacana.
The pine forest in some lower and warmer areas (not along this transect) is an association
of just P. oocarpa and P. pringlei.

7.Fir forest (2500-3000 m), with individuals of Abies
religiosa and A. hickelii to 30 m tall. On the highest cerro Teotepec there is
also a low forest of stout Pinus hartwegii; in rocky places grow Juniperus
monticola var. monticola and rosette and cushion species of the páramo.

The northern basically lowland portion of the Canyon of the Zopilote region is within
the Balsas Depression Floristic Province (Rzedowski 1978), a centre important for endemic
species and the spectacular diversification of Bursera species (Toledo-Manzur
1982). Most of the region is in the Middle Serranías Floristic Province, one of the major
centres for endemics in Mexico, which includes the genera Silviella, Omiltemia,
Microspermum, Peyritschia and Hintonella, and species such as Arracacia
ovata, Coaxana bambusoides and Donnellsmithia ampulliformis. Endemism
tends to be associated with high and humid locales, which function as isolated ecological
islands.

The flora of this region and the whole state are not thoroughly known. Inventories
suggest 30% of the 7000-7500 species in Guerrero are present. Some taxa have been more
completely collected and studied, e.g. pteridophytes, Pinaceae, Lauraceae, Fagaceae,
Melastomataceae, Araliaceae, Apiaceae, Rubiaceae and Orchidaceae. Arborescent ferns (e.g. Cyathea
divergens, Lophosoria quadripinnata) are widely distributed in the general
area. Peltogyne mexicana is a pre-Cenozoic tropical relict found in a few
populations, which is also known from Panama and Colombia (Sousa-S. and Delgado-S. 1993).
The taxonomic inventories illustrate the region's biological richness including 195 of the
207 estimated orchid species in Guerrero and half of the 351 collected species of
pteridophytes (Lorea 1990). In the Canyon of the Zopilote occur 20 of the 64 species of
Burseraceae reported for all of Mexico.

The region is very rich in timber resources. For general purposes including fuelwood,
most used are the pines and oaks Pinus ayacahuite, P. devoniana (P.
michoacana), P. chiapensis, P. herrerae, Quercus uxoris and Q.
laurina, and as well Abies religiosa and A. guatemalensis; for
particular construction, the palm Brahea dulcis, Cordia elaeagnoides and Pithecellobium
dulce; and for artisanry and carvings, the preceding two hardwoods and Actinocheita
potentillifolia.

Some species are used in local ceremonies, such as Bursera copallifera
("copal") and Solandra spp. ("copa de oro"). Among medicinals
are Ternstroemia pringlei ("té de tila"), Juniperus flaccida, Magnolia
schiedeana and Chiranthodendron pentadactylon ("flor de la manita") -
which is now cultivated in Europe and U.S.A.

The Canyon of the Zopilote region harbours abundant diverse fauna, also not well known.
A study of birds nearby to the south-west in the Sierra de Atoyac de Alvarez found 161
species, with 21 endemics (Navarro-Sigüenza 1986). Another study in that sierra reported
339 species of butterflies, 76% of the species known in Guerrero (Vargas 1990). The canyon
is one of nine Mexican areas rich in endemic butterflies (Llorente-Bousquets and
Luis-Martínez 1993). In Omiltemi Ecological State Park there are 37 species of amphibians
and reptiles, with 13 endemics (Muñoz-Alonso 1988).

The Canyon of the Zopilote River is within the Sierra Madre del Sur of Guerrero and
Oaxaca Endemic Bird Area (EBA A12), which has nine bird species of restricted range. Three
of the four threatened birds within the EBA have significant populations in the canyon -
the white-tailed hummingbird (Eupherusa poliocerca), short-crested coquette (Lophornis
brachylopha) and white-throated jay (Cyanolyca mirabilis).

Proper management of the mesophyllous montane forests is essential to maintain their
catchment of rainfall. For example, the Omiltemi forest captures over half the water for
the city of Chilpancingo. The number of indigenous people inhabiting the region is small,
in dispersed communities. They grow subsistence crops, and their impact on the vegetation
is minimal.

The region also has archaeological importance. Xochipala was a pre-Hispanic ceremonial
centre in 965 AD (Schmidt 1986). The northern area between Mezcala and Tetela del Río has
evidence of human settlements of the Preclassic, Protoclassic, Classic and Postclassic
periods (Rodríguez 1986). The regional variety thus offers potential for tourism, for
example from Acapulco, Chilpancingo and Mexico City.

The region is accessible by all the major means of transportation. The general area's
much-used major highway from the interior to the coast extends through the canyon and near
the eastern edge of the region, and a railroad from the north terminates near the region's
northern border at the Balsas River. From the south-west coast, a major road extends as
far as Puerto del Gallo and connects by minor road with the principal road west of
Chichihualco.

The Instituto Nacional de Investigaciones Forestales (INIF 1972) has pointed out the
region's importance for forestry, with the highest timber volume in the state - estimated
at 126-346 m3 per ha of coniferous forests with broadleaved trees (hardwoods)
present, 91-245 m3/ha of coniferous forests with hardwoods codominant, and
110-233 m3/ha of hardwood forests with conifers present. By 1971, Guerrero may
have provided up to 10.9% of Mexico's annual yield of saw timber (Styles 1993).

The state is fifth in Mexican coffee production, and the Canyon of the Zopilote region
produces c. 70% of Guerrero's coffee. In the extreme south-west, the natural forest canopy
has been left almost intact to shade the coffee plantations.

Farmers using the forest to shade their coffee plantations selectively cut mainly
species of Pinus, Quercus and Ficus. With the population increasing,
probably the road from Puerto del Gallo will be improved into a principal highway across
the region and the railroad will be extended across to the coast. However, the greatest
threat to the region is deforestation subsequent to commercial logging of coniferous and
hardwood trees for the lumber and paper industries, without reforestation, and as well
there is clandestine use by individuals. Many endemic species of flora and fauna are
threatened by the deforestation.

This region is one of the few large and highly diverse areas remaining in Mexico that
maintains relatively undisturbed native flora and fauna. Many plant communities still
occur that elsewhere have been greatly altered or destroyed. Already the region has become
a refuge for many threatened species.

Omiltemi Ecological State Park (17°31'-17°35'N and 99°30'-99°44'W) is 27 km west of
Chilpancingo, including 36 km² of the western portion of the Sierra de Igualatlaco. The
reserve was established in 1984 particularly for watershed management, through an
agreement of the state governor and the Universidad Nacional Autónoma de México (UNAM)
Facultad de Ciencias. Commercial export of Abies guatemalensis is prohibited by
Appendix I of CITES.

Botanists from the UNAM Department of Biology's Vascular Plants Laboratory, who have
been studying forests in Guerrero State for several years, suggest several communities
that need to be protected: (1) the Abies forest (30 km²) on cerros Teotepec and
Zacatonal (Map 16, zone C); (2) the adjacent area of mesophyllous
montane and subdeciduous tropical forests (100 km²) between Puerto del Gallo and Paraíso
(Map 16, zone A); (3) around Cerro Yextla (Map
16, zone B), by expanding Omiltemi park (30 km²) between Puerto Soleares and Cruz de
Ocote the park harbours c. 1.4% of Guerrero's mesophyllous forest, yet 11% could be
reserved in zones A and B; and (4) deciduous tropical forest in the Canyon of the Zopilote
River.